In the Oil & Gas industries, the continuous improvement in efficiency of machines like large turbo compressors is imperative. Design specifications of products like impellers are continuously updated to reach better performance and to improve durability.
Often, a design specification consists in the shape of portions of the final product, for example the shape of the vanes of an impeller. Also very often, the desired shape is achieved by machining of the workpiece.
Project requirements imply particular shapes, with tight tolerances. Consequently, machining requirements are very demanding.
Oil & Gas components are often machined through plunge milling. In plunge milling, as known, the machining is performed with a plurality of subsequent cylindrical milling operations. Such operations are carried out automatically under the control of an expert machinist. A control unit equips the machine tool, the machining program is loaded into the control unit for driving the spindle accordingly.
The number of workpieces to produce are significant, but not so large to justify other (much more expensive) manufacturing techniques. In this context, machinists are typically very skilled operators, their control is central to obtain a satisfying machining.
However, high requirements in machining prompted some research centers to develop software programs for determining the best conditions for perform the machining of a certain workpiece.
A first software program (some software programs of this kind are commercially available) provide stable cut conditions.
Such first software program receives as input the type of the material of the workpiece, the geometry of the machine tool, the engagement condition and the frequency response of the tool working on the workpiece. This information allows to calculate the work speed of the machine tool for machining the workpiece in stable conditions, to safeguard the workpiece and the tool itself. Typically, such information are integrated in the machining program. This first software program may provide machining information only if the engagement condition (in input) are steady during the machining of the workpiece.
But often the machining of a workpiece, in particular a workpiece for the Oil & Gas industry, requires different engagement conditions, due to the particular geometry of the workpiece and/or the shape of the machining.
A second software program (some software programs of this kind are commercially available) provides engagement conditions, to establish the feed of the machine tool. In practice, this software programs provides an array containing a plurality of engagement data of a plurality of corresponding points of the scheduled machining. In this way, a feed of the machine tool is assigned to each point of the scheduled machining. If the engagement data refer to steady engagement conditions during the machining, the stable cut conditions may be retrieved using the first software program. If the engagement data do not refer to steady engagement conditions during the machining (as it often happens), the stable cut conditions retrievable from the first software program are not reliable. In these cases, the work and the experience of the machinist is fundamental to understand the cut conditions during the machining. On the subjective basis of what he hears and sees during the machining of the workpiece, he corrects the speed of the machine tool to remain in the stable cut conditions.